The connection between abnormal protein phosphorylation and the cause or consequence of diseases has been known for over 20 years. Accordingly, protein kinases have become a very important group of drug targets. See Cohen, Nature, 1:309-315 (2002). Various protein kinase inhibitors have been used clinically in treating a wide variety of diseases, such as cancer, chronic inflammatory diseases, diabetes, and stroke. See Cohen, Eur. J. Biochem., 268:5001-5010 (2001), Protein Kinase Inhibitors for the Treatment of Disease: The Promise and the Problems, Handbook of Experimental Pharmacology, Springer Berlin Heidelberg, 167 (2005).
The elucidation of the intricacy of protein kinase pathways and the complexity of the relationship and interaction among and between the various protein kinases and kinase pathways highlights the importance of developing pharmaceutical agents capable of acting as protein kinase modulators, regulators, or inhibitors that have beneficial activity on multiple kinases or multiple kinase pathways. Accordingly, there remains a need for new kinase modulators.
The protein named mTOR (mammalian target of rapamycin), also known as FRAP, RAFTI or RAPT1, is a Ser/Thr protein kinase related to the lipid kinases of the phosphoinositide 3-kinase (PI3K) family. It functions as a sensor of mitogen, energy, and nutrient levels; and is a central controller of cell growth. mTOR has been shown to be one of the most critical proteins in the mTOR/PI3K/Akt pathway that regulates cell growth and proliferation. Georgakis and Younes, Expert Rev. Anticancer Ther. 6(1): 131-140 (2006). mTOR exists in two complexes, mammalian target of rapamycin complex 1 (mTORC1) which complexes with raptor, and mammalian target of rapamycin complex 2 (mTORC2) which complexes with rictor. While mTORC1 is sensitive to rapamycin analogs (such as temsirolimus or everolimus), mTORC2 is largely rapamycin-insensitive (Kim et al., Cell 110(2):163-175 (2002); Sarbassov et al., Science 307:1098-1101 (2005)).
Several mTOR inhibitors have been or are being evaluated in clinical trials for the treatment of cancer. For example, temsirolimus was approved for use in renal cell carcinoma in 2007 and sirolimus was approved in 1999 for the prophylaxis of renal transplant rejection. Everolimus was approved in 2009 for renal cell carcinoma patients that have progressed on vascular endothelial growth factor receptor inhibitors, in 2010 for subependymal giant cell astrocytoma (SEGA) associated with tuberous sclerosis (TS) in patients who require therapy but are not candidates for surgical resection, and in 2011 for progressive neuroendocrine tumors of pancreatic origin (PNET) in patients with unresectable, locally advanced or metastatic disease. The interesting but limited clinical success of these mTORC1 compounds demonstrates the usefulness of mTOR inhibitors in the treatment of cancer and transplant rejection, and the increased potential for compounds with both mTORC1 and mTORC2 inhibitory activity.
The preparation and selection of a solid form of a pharmaceutical compound are complex, given that a change in the solid form may affect a variety of physical and chemical properties of the compound, which may in turn provide benefits or drawbacks in processing, formulation, stability, and bioavailability of the compound. Potential pharmaceutical solids include crystalline solids and amorphous solids. An amorphous solid is characterized by a lack of long-range structural order, whereas a crystalline solid is characterized by structural periodicity. The desired class of pharmaceutical solids depends upon the specific application; an amorphous solid is sometimes selected on the basis of, e.g., an enhanced dissolution profile, while a crystalline solid may be desirable for properties, such as physical or chemical stability. See Vippagunta et al., Adv. Drug. Deliv. Rev., 48:3-26 (2001); Yu, Adv. Drug. Deliv. Rev., 48:27-42 (2001).
Whether crystalline or amorphous, potential solid forms of a pharmaceutical compound may include single-component solids. A single-component solid contains essentially the pharmaceutical compound in the absence of other compounds. Variety among single-component crystalline materials may potentially arise, e.g., from the phenomenon of polymorphism, wherein multiple three-dimensional arrangements exist for a single pharmaceutical compound. See Byrn et al., Solid State Chemistry of Drugs, SSCI, West Lafayette (1999). The importance of polymorphs in pharmaceuticals was underscored by the case of Ritonavir, an HIV protease inhibitor that was formulated as soft gelatin capsules. About two years after the product was launched, the unanticipated precipitation of a new, less soluble polymorph in the formulation necessitated the withdrawal of the product from the market until a more consistent formulation could be developed. See Chemburkar et al., Org. Process Res. Dev., 4:413-417 (2000).
Notably, it is not possible to predict a priori if crystalline forms of a compound even exist, let alone how to successfully prepare them (see, e.g., Braga and Grepioni, 2005, “Making crystals from crystals: a green route to crystal engineering and polymorphism,” Chem. Commun.: 3635-3645 (with respect to crystal engineering, if instructions are not very precise and/or if other external factors affect the process, the result can be unpredictable); Jones et al., 2006, Pharmaceutical Cocrystals: An Emerging Approach to Physical Property Enhancement,” MRS Bulletin 31:875-879 (At present it is not generally possible to computationally predict the number of observable polymorphs of even the simplest molecules); Price, 2004, “The computational prediction of pharmaceutical crystal structures and polymorphism,” Advanced Drug Delivery Reviews 56:301-319 (“Price”); and Bernstein, 2004, “Crystal Structure Prediction and Polymorphism,” ACA Transactions 39:14-23 (a great deal still needs to be learned and done before one can state with any degree of confidence the ability to predict a crystal structure, much less polymorphic forms)). The preparation of solid forms is of great importance in the development of a safe, effective, stable, and marketable pharmaceutical compound.
Citation or identification of any references in this disclosure is not to be construed as an admission that the references are prior art to this disclosure.